In dentistry a variety of devices are available which allow for preparation and/or application of dental materials in a dentist's practice. In particular for preparation of materials that are typically used in larger amounts, like for example dental impression materials, devices have been developed that provide for automatic dispensing from packages and/or for mixing of such materials. An exemplary device for mixing and dispensing a dental impression material is for example available under the designation 3M™ ESPE™ Pentamix™ from 3M ESPE AG, Germany. Typically such a device allows for two material components to be simultaneously supplied from a package through a mixer where they are mixed. Often the devices provide for continuously extruding the components through a mixer, where the components are mixed as the components flow through the mixer and released from an outlet.
The devices further typically have a motor driven piston for extruding the material from a container. Some motor driven devices implement drive concepts providing for driving the piston at different modes. For example in a first mode the material may be dispensed by slow movement of the piston at high forces, and in a second mode the pistons may be movable fast for enabling quick service operations, like material exchange or cleaning, for example.
For example U.S. Pat. No. 5,286,105 A discloses a device for mixing and dispensing two-component materials. The device has two pistons which can be advanced in cartridges by an electric motor via a magnetic clutch. When the motor is switched off and the clutch is disengaged, the pistons may be manually retracted and re-advanced by a hand wheel relatively quickly, for example for exchanging the cartridges in the device.
Further U.S. Pat. No. 6,168,052 B1 discloses an electrically driven dispensing appliance acting via drive screws on thrust plates for dispensing material from cartridges. The drive screws are axially stationary and act on the thrust plates. The electric drive comprises a first gear motor for a drive under high load during advance and relief, and a second motor for the drive under lower load during the retracting and fast advance motions. During advance and relief the drive screws are coupled to the first gear motor by a coupling, and during retracting and fast advance motions the drive screws are decoupled from the first gear motor but driven by the second gear motor.
Although available mixing and dispensing devices provide certain advantages there is still a need for a relatively inexpensive device, but which is operable relatively conveniently. Further a desirable dispensing device preferably is relatively reliable, and compact in design.